The present invention relates generally to integrated circuits, and, more particularly, to a voltage regulation system for an integrated circuit (IC).
Integrated circuits (ICs) include various circuit components, such as resistors, transistors, and inductors on a single chip. These circuit components are used to form logic circuits. Power is distributed to the logic circuits using a network of conductors. There are two types of such networks: power grids and ground grids. With the advent of micron-sized ICs, the size of the power and ground grids and the IR drop of the ICs have increased. Typically, the logic circuits are powered by a supply voltage signal. The supply voltage signal is transmitted to the logic circuits using the power grid. The ground grid supplies a ground voltage signal to the logic circuits. Each logic circuit is connected between nodes of the power and ground grids. The logic circuits receive the supply voltage signal at a first node of the power grid (hereinafter referred to as a ‘supply cold point’). There is a minimum IR drop in a first voltage level of the supply voltage signal at the supply cold point. The circuit components between the nodes of the power grid cause IR drops in the first voltage level of the supply voltage signal. As a result, the supply voltage signal received at a second node of the power grid (hereinafter referred to as a ‘supply hot point’) has a second voltage level that is less than the first voltage level by a voltage level equal to the IR drop at the supply hot point.
Similarly, the logic circuits receive a ground voltage signal first at a first node of the ground grid (hereinafter referred to as a ‘ground cold point’). There is minimum IR drop in a first voltage level of the ground voltage signal received at the ground cold point. The circuit components of the ground grid introduce IR drops in the ground voltage signal that cause a rise in the first voltage level of the ground voltage signal. As a result, the ground voltage signal received at a second node of the ground grid (hereinafter referred to as a ‘ground hot point’) has a second voltage level that is greater than the first voltage level by a voltage level equal to the IR drop at the ground hot point.
Typically, the first and second voltage levels of the supply voltage signal supplied to the IC are required to be within a predetermined range. If the first voltage level of the supply voltage signal at the supply cold point exceeds the highest predetermined voltage level of this range, then the IC may be damaged. Similarly, if the second voltage level of the supply voltage signal at the supply hot point is less than the lowest predetermined voltage level of the range, then the timing of critical paths of the IC can be affected, which may increase the functional timing of the IC. A difference between the highest and lowest voltage levels of the supply voltage signal is shrinking with the decreasing size of ICs.
Voltage monitor and regulator circuits are used to monitor and regulate the first and second voltage levels of the supply voltage signal. A voltage regulator provides the supply voltage signal to the supply cold point and regulates the first and second voltage levels of the supply voltage signal within the predetermined voltage range. FIG. 1 shows an IC 100 that includes a power grid having a plurality of supply and ground voltage lines, first and second logic circuit modules 102 and 104, first and second sets of circuit components 106 and 108, a resistor-ladder network 110, and a voltage regulator 111. The voltage regulator 111 includes an amplifier 112, a bipolar junction transistor (BJT) 114, a first resistor 116, and a capacitor 118. The resistor-ladder network 110 includes second and third resistors 120 and 122.
A first supply voltage line includes first and second nodes (N1 and N2). The first set of circuit components 106 is connected between the first and second nodes (N1 and N2). The first node (N1) receives a first supply voltage signal with no IR drop and the second node (N2) receives a second supply voltage signal that has a voltage level equal to a difference between the voltage level of the first supply voltage signal and a voltage drop across the first set of circuit components 106. A first ground voltage line GND1) includes third and fourth nodes (N3 and N4). The second set of circuit components 108 is connected between the third and fourth nodes (N3 and N4). The third node (N3) receives a first ground voltage signal (GND1) with no IR drop and the fourth node receives a second ground voltage signal (GND2) that has a voltage level equal to a sum of the voltage level of the first ground voltage signal and a voltage rise across the second set of circuit components 108.
The first logic circuit module 102 is connected between the first and third nodes (N1 and N3), and the second logic circuit module 104 is connected between the second and fourth nodes (N2 and N4). A first terminal of the second resistor 120 of the resistor-ladder network 110 is connected to the second node (N2) for receiving the second supply voltage signal. A second terminal of the second resistor 120 is connected to a first terminal of the third resistor 122 to form a voltage tap. A sense voltage signal is generated at the voltage tap. A second terminal of the third resistor 122 is connected to ground. The amplifier 112 has an inverting terminal connected to the voltage tap for receiving the sense voltage signal, a non-inverting terminal for receiving a reference voltage signal (Vref), and an output terminal for outputting an error voltage signal. The BJT 114 has a base terminal connected to the output terminal of the amplifier 112 for receiving the error voltage signal, a collector terminal for receiving an external third supply voltage signal, and an emitter terminal connected to the first node (N1) for providing the first supply voltage signal thereto and to ground by way of the capacitor 116 and the resistor 118.
In operation, the first logic circuit module 102 receives the first supply voltage signal at the first node from the voltage regulator 111 and the first ground voltage signal at the third node. The first ground voltage signal is at zero voltage level. Hence, a voltage across the first logic circuit module 102 equals the voltage level of the first supply voltage signal. The second logic circuit module 104 receives the second supply voltage signal at the second node and the second ground voltage signal at the fourth node. The second ground voltage signal has a non-zero voltage level, and hence a voltage across the second logic circuit module 104 equals a difference between the voltage levels of the second supply and ground voltage signals. As previously mentioned, voltage levels across the first and second logic circuit modules 102 and 104 are required to be within a predetermined voltage range for normal operation of the IC 100. The voltage level across the first logic circuit module 102 and the second logic circuit module 104 should be less than a first predetermined voltage level of the predetermined voltage range and should be more than a second predetermined voltage level of the predetermined voltage range, respectively. The resistor-ladder network 110 receives and scales the second supply voltage signal and outputs the sense voltage signal at the voltage tap. The amplifier 112 receives the sense voltage signal and generates the error voltage signal based on a comparison of the sense voltage signal with the reference voltage signal. The error voltage signal represents an IR drop in the voltage level of the first supply voltage signal. The BJT 114 receives the error voltage signal and regulates the voltage level of the first supply voltage signal such that the voltage levels across the first and second logic circuit modules 102 and 104 are within the predetermined voltage range.
However, the voltage regulator 111 senses only the second voltage level of the supply voltage signal received at the supply hot point, thereby not accounting for the rise in the first voltage level of the ground voltage signal at the ground hot point. When the voltage regulator 111 is an external voltage regulator, the voltage regulator 111 senses the supply voltage signal from the printed circuit board (PCB) and not the IC. The second voltage level of the supply voltage signal of the IC is less than that of the PCB. As a result, the first voltage level of the supply voltage signal is incorrectly regulated and may not be within the predetermined voltage range, which could damage the IC. Moreover, due to regulator-load regulation, the first voltage level of the supply voltage signal changes when a load current of the voltage regulator 111 changes, thereby increasing an output spread of the voltage regulator and decreasing the accuracy of the regulator. As a result, regulation of the first voltage level of the supply voltage signal within the predetermined range becomes difficult. When the voltage regulator 111 is an internal voltage regulator, the amount of heat dissipated increases the inefficiency of the voltage regulator and packaging cost of the IC.
Therefore, it would be advantageous to have an integrated circuit that includes a voltage regulator circuit with very low variation in the output voltage signal.